The present invention relates to general purpose modulators for communication systems. More specifically, the present invention relates to accurate, versatile digitally implementable modulation schemes.
The current need for communications has lead to a congestion of the limited number of presently available telecommunication frequency bands. This has placed significant demands on the modern communication system in that it has to operate effectively in an increasingly crowded spectrum. The modern communication system has to operate within a narrow frequency band while rejecting interference from adjacent bands. As the ability of a communication system to operate effectively within such an environment is dependent, in no small measure on the efficacy of its modulation scheme, the current demands on such systems have necessitated the development of ever more sophisticated modulation techniques. In effect, the demanding nature of modern communications systems, of which satellite, microwave, and telephone line systems are typical, has made implementation precision a key issue in modern modem technology. Moreover, new applications such as aeronautical and land mobile satellite systems, require modulation schemes which exhibit both spectral and power efficiency. There is therefore a need in the art for a generalized implementation scheme that offers improved performance in precision and efficiency.
In addition, ease of construction and suitability for economical mass production are important considerations in the selection of a modulation technique for a given application. Analog realizations of such circuits typically lack the desired degree of precision and flexibility to meet the challenges of the current telecommunications market. For this reason, digital implementation techniques are steadily gaining popularity. Within this framework, there is a further need in the art for a digitally implementable system which provides a modulation scheme which may be quickly and easily changed to accommodate many of the currently used signaling techniques or upgraded to incorporate new introductions in modulation technology.